Passive optical networks (PONs) have user or customer end devices and operator end devices in communication with each other. PONs may employ time-division multiplexing, in which end users share a wavelength in different time periods to communicate with the operator end (e.g., optical line termination (OLT)) via an upstream link. Accordingly, some transmitters on the user or customer side, such as those in an optical network unit (ONU), may have lasers working in a burst mode. In the burst mode, an ONU transmitter may be assigned a small time period and may send upstream signals only within its own time period. At other times, the ONU transmitter may have a bias current (or voltage) below its threshold current value (e.g., zero bias current), and therefore stay inactive.
When a burst-mode laser is enabled, it may emit or transmit an optical signal, on which radio frequency (RF) signals may be added. During emission, a temperature of the laser chip may increase slowly, causing the optical wavelength to drift or shift. In a time- and wavelength-division multiplexing (TWDM)-PON system that shares both time and wavelengths, multiple wavelengths may be used in both a downstream direction and an upstream direction. In the upstream direction, for example, a demultiplexer (DeMUX) may be used to separate different wavelengths sent from multiple ONUs. Each output channel in the DeMUX, similar to a filter, may have pass bands of various shapes such as a flat shape or a Gaussian shape. The wavelength shift of an optical signal during a burst period may cause problems at the filter. For example, if the peak-intensity wavelength of the optical signal is close to an edge of the filter pass band, after wavelength shift a portion of the optical signal may be filtered out because the shifted wavelength falls out of the pass band. The optical signal may consequently vary in power, which may cause data error problems. Therefore, the wavelength shift of burst-mode lasers is a problem to be solved.